27.31 : Small Intestine

The small intestine is a tubular structure extending from the pyloric sphincter of the stomach to the ileocecal valve of the large intestine.

This long, tubular structure has internal circular folds, giving it an enormous surface area. For this reason, the small intestine is the main organ responsible for digestion and absorption in the body.

Anatomically, it is divided into three parts — the duodenum, jejunum, and ileum.

The duodenum is the closest segment to the stomach, wrapped in a C-shape around the pancreas.

This is where chyme mixes with the digestive secretions from the pancreas and liver.

The jejunum follows the duodenum and leads to the ileum. The majority of chemical digestion and nutrient absorption takes place in the jejunum.

The ileum is the last and longest part of the small intestine, connecting to the large intestine at the ileocecal valve.

Both the jejunum and ileum, encircled by the large intestine, are located in the central and lower abdomen. They are suspended by a fan-shaped mesentery from the posterior abdominal wall.